The present invention relates to a multi-color electrostatic copying apparatus. Although illustrated and described as being applied to a two color apparatus, the present invention is not so limited and may be applied to an apparatus for copying in three or more colors.
In such an apparatus, a bipolar electrostatic image formed on a dielectric member is sequentially developed by toners of first and second different colors to form a bicolor toner image which is transferred and fixed to a copy sheet. The problem is that a small amount of the first toner is scraped off the dielectric member during the second developing step and becomes mixed with the second toner. Although the amount of mixed first toner is small, it can accumulate with time and degrade the color and electrostatic charge of the second toner image. The dielectric member may be a photoconductive drum or belt in which case the electrostatic image is formed through localized photoconduction or may be a non-photoconductive member in which case the electrostatic image is formed through electrostatic induction.
In a copying apparatus using liquid toners, the first toner may be removed from the second toner by making use of an electrostatically charged, non-image area of the dielectric member. However, this expedient is not usable in a dry copying apparatus.